Award: OCE-2023618

Intellectual merit Food webs are generally thought to move in one direction: smaller animals are eaten by larger animals. It was recently hypothesized that parts of marine food webs might move in the opposite direction. Specifically, large, marine fishes release hundreds of millions of eggs during their spawning aggregations. These eggs are highly concentrated in essential fatty acids, making them an especially valuable food resource (an egg boon). Those eggs are likely consumed by animals that are smaller and lower in the food web than the fishes that produced the eggs, representing a counter-gradient flow of energy in the food web. Food web studies have traditionally focused on the movement and transformations of carbon and stable isotopes, but recent studies have suggested that following fatty acids may provide new insights. This research project was the first rigorous test of this new counter-gradient flow hypothesis, and it tested this hypothesis using fatty acids and stable isotopes as tracers. This project examined an egg boon produced by Red Drum. It had two main components: (1) laboratory experiments to validate the use of fatty acids as tracers, and (2) field collections and biochemical analyses of animals to apply the tracers and address the hypothesis. The laboratory experiments used species that were smaller and lower in the food web than Red Drum (comb jellies, shrimp, crabs, fishes)to determine whether those species consumed red drum eggs, to determine which fatty acids could be used as tracers, and to assess how long after consuming eggs those tracers were useful. Results showed that many fatty acids are reliable tracers of egg consumption. Fatty acids from fish eggs persisted for short periods of time (2-5 days) in comb jellies and fishes, but lasted longer in crabs and shrimp (at least 5-10 days). It is well established that animals at higher levels in the food web have more enriched nitrogen isotopes than animals at lower levels. The experiments confirmed this for some smaller egg consumers, such as crabs, shrimp, and one forage fish (pinfish). Together, the laboratory experiments showed that fatty acids and nitrogen isotopes can be used to trace recent egg consumption in several species. Application of the tracers to animals collected in the field during the red drum spawning season confirmed that several species of comb jellies, jellyfish, and fishes exploited the Red Drum egg boon. These observations support the hypothesis that fish spawning aggregations provide a pathway in marine ecosystems for a counter-gradient flow of nutrients from larger to smaller organisms. Further, since eggs have exceptionally high concentrations of essential fatty acids, which all animals require for adequate nutrition, egg consumption appears to play an important role in redistributing essential fatty acids through marine food webs. Broader impacts The importance of egg production by one species to the vitality of populations of other species has rarely been considered by scientists or resource managers. Recognizing the role of egg boons in marine food webs could lead to better management decisions for marine species and ecosystems, particularly for species that are of conservation concern or of commercial importance. For example, it may be prudent to adjust harvest limits on adult fishes not only to maintain those populations, but also to ensure that populations of egg consumers have a supply of the nutrients that are supplied by eggs. To date, the project has one peer-reviewed publication, with another paper in development. All the data generated through this project has been submitted to be made publicly available by 2024. This includes a large number of fatty acid profiles and stable isotope signatures for a variety of species. Such a database will be valuable to researchers who are investigating fatty acids and stable isotopes in marine systems. This project substantially advanced the professional training of two early career, female scientists. Co-PI Nair, who aspires to a position in academia, received broad training in all aspects of research and research administration, which will elevate her competitiveness for permanent positions. It also provided her with significant new experience and expanded her professional network. Research Assistant Miller learned many research skills and elevated her desire to pursue a career in science. She is now pursuing a graduate degree in fishery science. Research findings were disseminated through several national and international conferences. Project personnel used the project subject matter and activities to augment the training of K-12 STEM education professionals. Two, 3-day Teacher On The Estuary workshops gave teachers the opportunity to conduct hands-on field activities and learn about food webs, fatty acids, and stable isotopes in marine ecosystems through classroom-based lessons. This helped the educators understand the scientific endeavor, from hypothesis to data collection and analysis. The direct experience teachers gained during the workshops allowed them to bring real world research experiences and environmental STEM concepts into their classroom, laboratory, and field programs. Last Modified: 11/30/2023 Submitted by: LeeAFuiman